As means for preventing drunken driving, it has been tried to mount an alcohol interlocking device on an automobile in recent years. In an alcohol-drinking detecting device utilizing a breath, however, there is such a concern that the device can be deceived by the breath of a fellow passenger.
On the other hand, the present applicant has disclosed a method for arranging a pressure sensor in a seat cushion section and obtaining and analyzing a pulse wave of a breech of a person to estimate the state of the person as a system which monitors a biological body state of a driver during driving in a non-invasive manner, for example, in Patent Literatures 1 to 3. Specifically, a maximum value and a minimum value of a time-series signal of a pulse wave are obtained by a smoothing differentiation method of Savitzky and Golay, respectively. The maximum value and the minimum value are obtained for each 5 seconds so that their mean values are obtained. Using a square of a difference between the respective mean values of the maximum values and the minimum values obtained as a power value, the power value is plotted for each 5 seconds so that a time-series waveform of the power value is produced. In order to read a global change of the power value from this time-series waveform, a slope of the power value regarding a certain time window Tw (180 seconds) is obtained by least-square method. Next, the slope regarding the next time window Tw is similarly calculated in an overlapped time TI (162 seconds) and the calculation results are plotted. A time-series waveform of the slope of the power value is obtained by repeating this calculation (moving calculation) sequentially. On the other hand, the maximum Lyapunov exponent is obtained by applying Chaos analysis to the time-series signal of the pulse wave, a maximum value is obtained by a smoothing differentiation method like the above, and a time-series waveform of a slope of the maximum Lyapunov exponent is obtained by conducting moving calculation. Then, the time-series waveform of the slope of the power value and the time-series waveform of the slope of the maximum Lyapunov exponent take phases opposite to each other, and a waveform having a large amplitude at a low frequency in the time-series waveform of the slope of the power value is determined as a characteristic signal indicating a sleep prediction and a point at which the amplitude has become small thereafter is determined as a sleep point.
Further, as Patent Literature 4, a system provided with an airbag (air pack) including a three-dimensional solid fabric inserted therein, where the air pack is disposed at a site corresponding to a waist portion of a person, an air pressure fluctuation in the air pack is measured, a biological signal of the person is detected from the time-series waveform of the air pressure fluctuation obtained, and the biological body state of the person is analyzed is disclosed. Further, in Non-Patent Literatures 1 and 2, trials for detecting a biological signal of a person by disposing an air pack sensor along a lumber iliocostal muscle are reported. A pulse wave near a lumber area shows a circulation fluctuation of blood flowing in a descending aorta according to a heartbeat, where a state change of a person corresponding to a heartbeat fluctuation can be captured more accurately in utilization of this aortic pulse wave than in utilizing the breech pulse wave disclosed in Patent Literatures 1 and 2.
The present applicant has reported that it is possible to determine presence/absence of alcohol in the body by further developing the techniques described in Patent Literatures 1 to 4 and Non-Patent Literatures 1 and 2 and performing frequency analysis of a pulse wave obtained from an air-pack sensor as Non-Patent Literature 3.